The invention relates to a device for generating electromagnetic radiation in the ultraviolet range of the electromagnetic spectrum, which device is equipped with an at least partly transparent discharge vessel whose discharge space is filled with a gas filling, with means for triggering and maintaining an excimer discharge in the discharge space, and with a luminescent material that contains a UV-C emitting phosphor.
Radiation sources of this kind are suitable, depending on the spectrum of the radiation emitted, for general and auxiliary lighting, e.g. domestic and office lighting, for the back-lighting of displays, e.g. liquid crystal displays, for traffic lights and signal lighting, and for photochemical processes, e.g. sterilization and photolysis.
This invention is particularly concerned with devices useful for disinfection and purification of fluids and surfaces.
There are many known techniques for disinfecting and purification of fluids and surfaces, including the use of chemical or physical agents, mechanical means, and UV radiation. Of these, the traditional method of disinfection has been the use of chemical agents in the form of chlorine. Growing concerns about chlorine's safety and effect on the environment have promoted the evaluation of other disinfection and purification methods.
To date, the most viable alternative to chlorine disinfection is ultraviolet (UV) disinfection. Ultraviolet light has a proven track record of killing bacteria and viruses found in municipal wastewater. Improvements in ultraviolet-lighting technology have led to the development of UV systems that also treat spent metalworking fluids in the industrialized world; disinfect drinking water in developing countries; and clean aquaculture water, ballast water, and hospital air everywhere.
Such UV-emitting devices are known from U.S. Pat. No. 6,398,970, disclosing a device for disinfecting water comprising a gas discharge lamp including a discharge vessel with walls composed of a dielectric material, comprising a first electrode on the outer surface of said walls and a second electrode, said discharge vessel containing a xenon-containing gas filling, wherein the walls are provided, at least on a part of the inner surface, with a coating containing a phosphor emitting in the UV-C range. The phosphor comprises an activator selected from the group consisting of Pb2+, Bi3+ and Pr3+ in a host lattice.
A disadvantage of the known UVC-emitting devices described in U.S. Pat. No. 6,398,970 is that the optical efficiency achieved is not at optimum for germicidal applications, such as disinfection and purification of fluids and surfaces.
It is known, that the efficiency of the UVC emitting devices is both dose related and wavelength dependent.
Ultraviolet light is classified into three wavelength ranges: UV-C, from about 200 nm to about 280 nm; UV-B, from about 280 nm to about 315 nm; and UV-A, from about 315 nm to about 400 nm.
Generally, UV light, and in particular, UV-C light is “germicidal” i.e., it deactivates the DNA of bacteria, viruses and other pathogens and thus destroys their ability to multiply and cause disease, effectively resulting in sterilization of the microorganisms. But the germicidal effect of ultraviolet light, as shown by the germicidal action curve (GAC) in FIG. 17, occurs especially in the wavelength range from 200 to 300 nanometers. UV light with a wavelength λ approximately between about 250 to about 260 nm provides the highest germicidal effectiveness.
It was concluded that wavelength was an important consideration in these treatment systems and therefore it is an object of the present invention to provide a device for generating ultraviolet radiation in a wavelength range, that is ideally suited to germicidal processes.